In organic EL (electro luminescence) display devices such as organic EL displays and in liquid crystal display devices such as liquid crystal displays (LCDs), a retardation film having a controlled optical anisotropy is used for the purpose of optical compensation, and materials such as polycarbonates and cyclic polyolefins have been mainly used for the retardation film. In recent years, of these cyclic polyolefins, norbornene-based ring-opening copolymers using highly reactive norbornene derivatives as precursors have attracted attention, and retardation films have been developed which utilize various kinds of norbornene-based ring-opening copolymers.
For example, Japanese Unexamined Patent Application Publication No. 2008-52119 (PTL 1) discloses a reverse dispersion retardation film containing a norbornene-based ring-opening polymer obtained from a specific norbornene derivative with a controlled endo/exo ratio. However, the reverse dispersion retardation film made of the conventional norbornene-based ring-opening polymer described in PTL 1 is not necessarily sufficient in terms of heat resistance. In addition, Japanese Unexamined Patent Application Publication No. 2005-290048 (PTL 2) and Japanese Unexamined Patent Application Publication No. 2008-7733 (PTL 3) disclose norbornene-based ring-opening copolymers obtained by using norbornene derivatives having specific spiro rings. However, when films are formed by using the conventional norbornene-based ring-opening copolymers described in PTLs 2 and 3, retardation films having optical characteristics such as reverse dispersion characteristics or negative A characteristics cannot necessarily be obtained. Note that, when a film which does not have reverse dispersion characteristics but has low-birefringence characteristics is used for a retardation film, the thickness of the film needs to be sufficiently large. For this reason, the conventional norbornene-based ring-opening copolymers described in PTLs 2 and 3 are not necessarily sufficient also in terms of costs for film production and of thin film formation. Accordingly, the retardation films utilizing the conventional norbornene-based ring-opening copolymers are still insufficient in terms of achievement of both heat resistance and optical characteristics.